Polymerase chain reaction $(PCR)$ is a process used for the amplification (copy small segments) of $DNA$. It is a technique for enzymatically replicating $DNA$ without using living organisms, such as $\mathrm{E}$. coli or yeast. It is commonly used in the nedical and biological research labs for a variety of tasks, like detection of ereditary diseases, the identification of genetic fingerprints, diagnosis of infectious diseases, cloning of genes, paternity testing etc. segments and number of repetitive units.